Fire resistant pulp board



Patented Feb. is, 1938 UNlTED STATES PATENT Homasote Company,

Jersey No Drawing. Application March Serial No. 71,535

12 Claims.

My invention relates to a pulp board which is highly fire-resistant andto the method of making the same;

-My invention is of particular advantage in 5. connection with moldedpulp board, such as is usually nmde by running wood pulp, paper pulp orthe like into a mold and'by means of pressure removing the majority ofthe water (see, for instance, United States Letters Patent No. 971,936,

dated October 4, 1910, and No. 1,272,566 dated July 16, 1918) andsubsequently drying out the,. remainder of thewater by the applicationof heat. After it has been dried, or simultaneously with the drying, theboard may, if desired, be

subjected to high pressure in order to compact the same thus giving ithigher tensile and transverse strength-and a higher degree of hardness.The

object of my invention is to produce a pulp board whose fibres arecoated with aluminum hydrate to such an extent that the board is highlyfire-resistant and will smolder as little as possible, if at all, afterhaving been exposed to a flame, which contains a substantial proportionof incombustible substances, and which has a surface suflclently hard toresist minor injuries.

- It is a further object of my invention to apply aluminum. hydrate tofibres in such a manner that when such fibres are molded or otherwiseformed into the preliminary shape of the finished 0 board there will beas little interference as possible with the drainage of the water fromthe pulp and no undue warping of the wet board.

()ther objects of my invention will be apparent from the followingdescription thereof.

35 In order to fireproof the pulp fibres in the best manner known to me,I deposit aluminum hydrate thereupon before they are shaped into theform of a board. I deposit such aluminum hydrate preferably in the formof a precipitate from a double 40 decomposition of an aluminum salt andof some ,fother' substance which willreact with such aluml num salt toform aluminum hydrate, but not such a substance-as will react'with thealuminum salt to form insoluble crystals. I-prefer to use alumlnumsulfate and caustic soda or, sodium alwminate, obtaining in each casealuminum hydrate and sodium sulfate, the latter in-the form of soldblecrystals which eventually will go out with the wash water. The aluminumhydrate when obtained as a precipitate from the double decompositionreferred to, is in a fine state of subdivision and will therefore morereadily coat each of the pulp fibres. I prefer to cause the reactionbetween the aluminum sulfate and the 55 caustic soda or other reagent totake place in the beater in which, and while, the pulp is being beaten.first adding the aluminum sulfate and. when this has been thoroughlydissolved in the beater, adding a suspension of caustic soda or othersuitable reagent, but I may cause such rea corporation of New action,and obtain the precipitated aluminum hydrate resulting therefrom, in aseparate vessel, ln which event the precipitate should'be used as soonas possible to prevent agglomeration thereof. The proportion of aluminumhydrate is preferably such as will result in as complete a coating of.the pulp fibres as possible, but not much more than that, so as not tointerfere with the proper felting thereof.

To the pulp which is being beaten in the beater, I add, preferablybefore adding the aluminum hydr te and other reagent, a substantialproporti n of fullers earth, although I may add this while thereaction'is taking place or even afterwards. Preferably at the same timeat which I add the fullers earth, I add to the pulp, while it is beingbeaten, a substantial proportion of en foliated vermiculite, although Imay do this at a later stage. Preferably, after the reaction has takenplace and before adding any sizing (if sizing be added) I add asubstantial proportion of asbestos fibres sufficiently short, forinstance, I /3 inch in average length, so as not to interfere with thesubsequent proper felting of the fibres and the pulp. The flbresareknown in the trade as asbestos floats. My reason for adding the asbestosfibres, if I add them at all, after the re- "action has been completed,is that I desire to have'the aluminum hydrate coat as fully as possiblethe fibres of the pulp, which must be fireproofed, the asbestos itself,of course, needing no fireproofing; also to have the asbestos fibresprotect the coated fibres. I prefer to render the board waterproof aswell as fire resistant, and therefore prefer to add to the beatenmixture of the ingredients hereinabove referred to, the usual soap(sizing) and thereafter to precipitate it ontothe fibres. A

After the materials hereinabove referred to have been thoroughly mixed,the board is shaped in a mold. or otherwise and dried. after which itmay, if desired, be compacted; or it may be simultaneously dried andcompacted, for instance, in a hot press, My present preferred formula isthe following, by weight:

. a Per "cent Pulp (dry) s 26 Aluminum hydrate"; e Asbestos 7 Fuller'searth I 2c Exfoliated vermiculite r.. '35.

This formula may be varied, not only by leavlog out the asbestos butalso by changing the proportions of the remaining ingredients. I haveobtained good results by using pulpidfy weight) to aluminum hydrate 6 to8%, asbestos 'l to 10%, fullers earth 25 to 30%, and exfoliatedvermiculite 30 to I I have already indicated that the asbestos may beomitted, although the board is very much improved by its presence. Inplace of fuller's earth I may use an equivalent material, such askaolin, or other finely divided clay, or bauxite, but I have not foundas yet any equivalent which is as. effective as fullers earth or nearlyso as bauxite; care should, however, be taken to use a fullersearth'which is not too dense-for instance, such as I have obtained fromEngland which, I understand, is of the density characteristic of thefuller's earths found in suchcountry, and isnot so effective because itis entirely too dense. The main purpose of using this material is notonly to avoid using in the fire-resistant board too much of thecombustible pulp, but also to assist in hardening the surface of thecompleted board. The purpose of using exfoliated vermiculite is toobtain very free drainage during the step of reor other suitablehygroscopic salt or sodium .thiosulfate, to produce a 2% or 3% solutionof this material with the water in the beater. The purpose of addingthis material is to guard against a deterioration of the aluminumhydrate covering of the individual fibres, if the board should be dried,or exposed to fire, for so long a time as would otherwise causesuchdeterioration. Of course, such overdrying should be avoided, ifpossible, but with the'addition of either one of these salts the dangerof the aluminum hydrate becoming porous or shrinking (because ofdehydration) thus exposing some of the fibre, is avoided.

My preferred method (which results in the let's?1 costly board)therefore includes the fol- 10 g steps:

1. Preparation of a pulp suspension from any suitable fibre, such aswood fibre, chemically digested fibre or mixtures thereof, as can beobtained, for instance, by beating up old newspapers; bagasse or strawmay be used in whole or in part. I refer to all such substances in myclaims as cellulosic fibres. Enough water should be used to permit thefibres to fiow freely.

2. Adding to 26 parts by weight of pulp (dry), as it is being beaten inthe beater, 26 parts by weight .of fullers earth and 35 parts by weightof exfoliated vermiculite, the beating continuing until all theingredients have. been thoroughly mixed.

4. Preparation of aluminum -hydrate in the requisite finely dividedform, in an amount just about suificient to coat the fibres, by addingaluminum sulfate to the beater and, when this is dissolved, adding .asolution of the requisite amount of sodium aluminate; Just about, enoughofthe latter substance should be used to convert the aluminum of thealuminum sulfate. into aluminum hydrate; I' prefer to use-thissubstance, as the combination of the sodium with the sulfate-ion willalso release aluminum hydrate contained in the sodium alumin'ate. It isadvisable that the solution of sodium aluminatebe added gradually to thesolution'of the aluminum sulfate, to give full opportunity to thealuminum hydrate particlu to coat fully the pulp fibres.

The beating should be continued during this step.

Enough aluminum sulfate and sodium alumi nate should beadded to resultin the formation of about 6 parts by weight of aluminum hydrate, keepingin'mind that aluminum hydrate is obtained not only from the reactionbetween the aluminum of the aluminum sulfate, but that the sodiumaluminate itself embodies aluminum hydrate.

As the pulp is to be subsequently sized, care should be taken to keep orrender the mixture in the beater neutral or slightly alkaline, so as toavoid premature precipitation of the soap.

4. Adding to the beater 9 parts of well shredded asbestos fibres, thefibres preferably not exceeding M; inch in length, to 26 parts by weightof pulp (dry), the beating being continued until the ingredients arethoroughly mixed.

5. A suitable rosin or other soap, in weight equal to about 2% to 3% ofthe total weight of the solid materials, is added to the beater chargeas a sizing ingredient, preferably after the asbestos, fullers earth andexfoliated vermiculite have been thoroughly mixed with the pulp.

6. The soap is then precipitated by adding a suitable quantity of asuitable precipitant, such as aluminum sulfate.

7. Calcium chloride (or magnesium chloride) is then added in an amountsui'ilcient to produce a solution of 2% strength with the water in thebeater.

1-7. Preferably the beatingof the pulp, and thereafter of the pulp andother ingredients as the latter are being added, continues throughoutthe first seven steps, so that a thorough mixture of the variousingredients is obtained.

8. The pulp is then shaped in a mold or otherwise, and dried, andcompacted. The drying time depends, of course, upon a number of factors,such as the thickness of the board and the amount of water containedtherein. Care should .be taken not to dry for so long a time as to overusein construction work exposed to the elements.

It has-rigidity and good mechanical strength with freedom frombrittleness. and a low heat transmission as compared with boardscomposed principally of mineral products, such as cement, asbestos orplaster. My invention may be employed, with substantially equally goodresults, in making a pulp board bythe laying up process, that is, byforming paper-like layers of the board, for

instance, on a paper making machine, and uniting the layers thereof inthe usual manner, for instance, with the aid of sodium silicate.

The proportions of material hereinabove given may be varied, as may alsothe steps and succession .of steps outlined in my statement of.preferred method, without departing from the spirit of my invention. Allof the proportions given hereinabove are approximate. 1

The aluminum hydrate, referred to by me, is

I claim:

1. A highly-fire resistant'lubstantially hard surface board comprisingcellulosic fibres coated with aluminum hydrate and mixed with asubstantial proportion of fullers earth and exfoliated vermiculite. a A

2. A highly fire resistant substantially hard surface board, as claimedin .claim 1, containing, by weight, cellulosic fibres 25 to 30 parts,aluminum hydrate 6 to 8 parts, fuliers earth 25 to 30 parts, andexfoliated vermiculite 30 to 40 parts.

.3. A highly fire resistant substantially hard surface board, as claimedin claim 1, comprising, by weight, cellulosic fibres approximately 26parts, aluminum hydrate approximately 6 parts, ful1er's earthapproximately 26 parts and exfoliated vermiculite approximately 36parts.

4. A highly fire resistant substantially hard surface board, as claimedin claim 1, containing also a substantial proportion of asbestos.

5.. A highly flre resistant substantially hard surface board as claimedin claim 1, comprising,

by weight,'cellulosic fibres 25 to 30 parts, aluminum hydrate 6 to 8parts, fullers earth 25 to 30 parts, exfoliated vermiculite 30 to 40parts, and

asbestos 7 to parts.

6. A highly fire resistant substantially hard surface board as claimedin claim 1, comprising by weight, cellulosic fibres approximately 26parts, aluminum hydrate approximately 6 parts,

fullers earth-approximately'26 parts, exfoliated vermiculiteapproximately 36 parts, and asbestos 7 parts.

7. A highly fire resistant substantially hard surface board as claimedin claim 1, containing also from 2% to 3% of a hygroscopic salt suitableto protect the aluminum hydrate from dehydration when exposed to heat. 4

8. A highly fire resistant substantially hard surface board as claimedin claim 1, containing by weight, cellulosic fibres 25 to 30 parts,aluminum hydrate 6 to 8 parts, fullers earth 25 to 30 parts, exfoliatedvermiculite 30 to 40 parts and from 2% to 3% of a hygroscopic saltsuitable to protect the aluminum hydrate from dehydration when exposedto heat. I

9. A highly fire resistant substantially hard surface board, as claimedin claim 1, comprising, by weight, cellulosic fibres approximately 26parts, aluminum hydrate approximately 6 parts,

fullers earth approximately 26 parts, exfoliated vermiculiteapproximately 36 parts and from 2% to 3% of a hygroscopic salt suitableto protect the aluminum hydrate from dehydration when exposed to heat.

10. A highly fire resistant substantially hard surface board, as claimedin claim 1, containing also a substantial proportion of asbestos andfrom hygroscopic salt suitable to protect the aluminum hydrate fromdehydration when exposed to heat. 12. A highly fire resistantsubstantially hard surface board, as claimed in claim 1, containing,

by weight, cellulosic fibres 26 parts,-aluminum hydrate 6 parts, fullersearth 26 parts, exfoliated vermiculite 36 parts, asbestos 7 parts andfrom 2% to 3% of a hygroscopic salt suitable to pro tect the aluminumhydrate from dehydration when exposed to heat.

. HUBERT L. BECHER.

